The present application relates to a longitudinal member for use in spinal or trauma surgery and a stabilization device with such a longitudinal member.
A dynamic stabilization system for segments of the spinal column which comprises a flexible rod made of an elastic material and bone anchors to anchor the rod in the vertebrae is known from EP 1 364 622 A2 and EP 1 527 742 A1, respectively. The material of the rod is a biocompatible polymer material, for example a material on the basis of polyurethane. The rod has a corrugated surface with the corrugations extending in a direction transverse to the rod axis.
Usually, the elastic rods are manufactured by injection molding whereby the molten plastic material is injected at high pressure into a mold which is the inverse of the desired shape. As shown in FIG. 1, after injection molding, the polymer chains 100 of the material are entangled and may include filling particles 101 and transverse links 102 between them. A rod 103 which is made by injection molding comprises an isotropic structure of the polymer chains and is therefore non homogeneous in a sense that it comprises defects in its macromolecular structure. The known elastomer rods exhibit a local flow of material when pressure is exerted onto their surface in the process of fixing the rod within a receiving part of a bone anchoring element. This local flow of material may cause a loosening of the fixation of the rod within the bone anchoring element.
Based on the above, there is a need to provide a longitudinal member for use in spinal or trauma surgery and a stabilization device using such a longitudinal member manufacturing which has improved mechanical properties as well as reduced manufacturing costs compared to the known polymer rods.